The aim of the present research is to evaluate the effectiveness of intensive and long-term operant conditioning on the modifiability of autonomic processes in rats. Using heart rate as the criterion response, the potential for long-term conditioning in the unrestrained animal will be achieved by fitting the rat with a telemetric device to monitor its heart rate. The resulting signal, appropriately treated, will be fed into a computer, which has the task of controlling the contingencies and recording the data. To avoid problems of satiation which result from apetitive reinforcers, intracranial brain stimulation will be employed as the reinforcing agent, also delivered by telemetry. The major questions of interest are: (a) What are the limits, in both directions, that heart rate can be driven by an intensive and long-term operant conditioning regime? (b) By appropriate manipulation of the reinforcement contingencies, can such induced changes in heart rate be made highly resistant to extinction? (c) And if so, can extinction of an induced change in heart rate be rapidly accomplished by reversing the reinforcement contingencies? The purpose of the present research proposal is to obtain pilot data bearing on these questions.